Small-flowered sand-verbena COSEWIC assessment and status report: chapter 16

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Addendum

Status of the Small-flowered Sand-verbena (Tripterocalyx micranthus) based on field data from 2002. This addendum was prepared by E. Haber based on information provided by Bonnie Smith that was available for designation purposes. This addendum contains only the basic population data, a revised technical summary and a revised figure 4.

Summary

Small-flowered sand-verbena (Tripterocalyx micranthus (Torr.) Hook.) is primarily distributed in southeastern Alberta (seven sites) in Canada. As well, the species occurs at one site just east of the Alberta border in southern Saskatchewan.

Small-flowered sand-verbena sites is documented at Lower Bow (789 plants), Purple Springs (269 plants), Grassy Lake (1797 plants) and North of Medicine Hat (100 plants estimated), North of Medicine Hat Suffield (100 plants), Lost River (100 plants estimated), Suffield National Wildlife Area (1 plant). The total population of four sites surveyed during the 2002 field season by the author was 2955 plants. The total population (counts and estimates) for all Alberta sites is 3156 plants. The Grassy Lake and North of Medicine Hat Suffield sites are new locations for the species not reported in the earlier report (Smith and Bradley 1992). In the process of conducting surveys, other areas of potential suitable habitat were also examined in and around the known sites. No plants were found at the Saskatchewan site during the 2002 field season.

Small-flowered sand-verbena sites are typically small in size usually not exceeding 100 sq. m. Population numbers can change dramatically from year to year based on climatic conditions, in particular, moisture levels. In 2001 the Lower Bow site contained 1 plant while in 2002 the same site contained 789 plants. Small-flowered sand-verbena is an ephemeral annual species which in good years produces masses of seeds that remain viable in the sandy seed bank until a future growing season with suitable climatic conditions.

Small-flowered sand-verbena is found in dry habitats, particularly in loose sands of dune and sandhill areas. Some element of active sand is usually required. The largest populations are on hard packed finer sand on level terrain but it also occurs on south, west, and east-facing slopes and along dune ridge tops. Most sites are on the uplands but the species may also occur in the valleys of the Lost and South Saskatchewan Rivers where sand dunes extend down into the valleys. It is restricted to the Dry Mixedgrass Subregion of the Grassland Natural Region - an area that has undergone extensive modification from its natural state by human activity.

Limiting factors of concern include the following: dune stabilization, changes in land use and invasion of weedy species. The Grassy Lake site, containing more than half of the plant’s Alberta population, is currently under threat as a result of sand removal and levelling of the main dune area. Considerable work on management strategies and population assessment should be undertaken as soon as possible as a means of maintaining the presence of this species in Alberta.

Population Size and Trends

Alberta

Summary

During the 2002 field season small-flowered sand-verbena sites were located at Lower Bow (789 plants), Purple Springs (269 plants), and Grassy Lake (1797 plants). The total population of Alberta plants counted by the author during the summer 2002 field season was 2855 plants. In addition, Trottier counted 100 plants at the North of Medicine Hat Suffield site. Macdonald (1994) reported 1 plant at the Suffield National Wildlife Area site. The Lost River site is reported as containing a small population, probably not exceeding 100 plants for the year 2000 (Wallis, pers. comm.). The North of Medicine Hat site originally located by Johnson is likely small in size and is estimated to contain a small population of approximately 100 plants. In total, the Alberta population is estimated to contain 3156 plants. Localities are indicated in the revised figure 4.

The population numbers for the 2002 field season are considerably higher most likely as a result of a greatly increased amount of precipitation. In 2001, a drought year, only one plant was counted (Lower Bow). The Grassy Lake site is a new location for the species. In the process of conducting surveys on known sites other areas of potential suitable habitat were also examined in and around the known sites. The Suffield National Wildlife Area site was not included in the 2002 survey as a result of access difficulties due to restrictive military protocols required to enter Canadian Forces Base Suffield.

In the original COSEWIC status report (Smith and Bradley 1992), small-flowered sand-verbena was known from five sites in Alberta. The sites were as follows: 1) Lost River, 2) Lower Bow, 3) Purple Springs, 4) South Saskatchewan River, north of Medicine Hat, and 5) Wolf Island. The total Alberta population of small-flowered sand-verbena was estimated to be under 1000 plants (Smith and Bradley 1992). At that time, the population was distributed amongst the southeastern Alberta localities as follows: Lost River - 200 plants, Bow Island - 265 plants, Purple Springs - 30 plants, North of Medicine Hat - less than 100 plants, Wolf Island - 110 plants.

As well, historically, small-flowered sand-verbena had been collected by Macoun from the crossing of Manyberries Creek, north of Milk River in 1895. This site has not been relocated.

The Lower Bow, Purple Springs, Wolf Island and Lost River sites were surveyed by Wallis and Wershler in 1987 (Wallis and Wershler 1988). Johnson surveyed the site north of Medicine Hat on the South Saskatchewan River in 1972 and 1973 (Johnson and Hallworth 1975). Macdonald surveyed the Suffield National Wildlife Area site in 1994 (Macdonald 1997). As well, Sharp and STG (collector) visited the Lost River site in 1972 and 1979, respectively (ANHIC 2001). Smith resurveyed all existing sites, except the Suffield Wildlife Area site, in 2001 (Smith 2002 pending).

Alberta Site Population Data - 2002

Grassy Lake (figure 4 site 2)

This site contains well over 50% of the known Alberta population of small-flowered sancounted during the 2002 field season. This site is of vital importance for ensuring the survival of the species in Alberta. Plants are found on a dune that rises 6 m from the surrounding plain. As well, plants are found on the surrounding sandy plain. Of the 1797 plants, 570 are found on the sand dune (60 of these on the open northeast dune face, the remainder on the dune crest and upper southwest facing dune slopes). A total of 1227 plants are found on the surrounding sandy plain (1070 of these south of the access road to the dune, the remainder north of the access road and south of the gas battery). Small-flowered sand-verbena disappears as the prairie becomes more stabilized with grasses and other herbs. The site is small in size, approximately 100 m (north to south) x 40 m (east to west). Small-flowered sand-verbena occurs with considerable density especially around and under the edges of Artemisia cana shrubs (Figure 5) on the open sandy plains east of the sand dune at this site. Plants on open sand can become 3-4 ft. in width (Figure 6), very large in comparison to other sites investigated during the 2002 field season.

Purple Springs (figure 4 site 3)

Small-flowered sand-verbena occurs at three areas along the dune. Area 1: western adjacent dune, 30% open sand - 60 plants along the upper dune areas and on open sand. Area 2: southern dune area of main dune. 30 m area of blowouts and open sand associated with bank swallow nest site. Population 197 plants. Area 3: northern dune area of main dune. 10 m area of exposed sand, bank swallow nest sites, ATV use and tracks up the dune face. Population 12 plants. Total population: 269 plants.

Typical small-flowered sand-verbena plants at area 3 are 4-6 inches in height. Plants at area 2 can be 2 ft. x 3 ft. in diameter at the largest.

Lower Bow (figure 4 site 4)

The population is distributed at three locations within a small dune field composed of about a dozen dunes. Two dunes within this field contain areas of open sand, blow-outs and bank swallow nests. Small-flowered sand-verbena is found on these two dunes, one of which is intersected by the gravel road which provides access to the site. The total population found on the western dune along the gravel road is 293 plants (area 1). An additional 2 plants were located on the portion of this dune separated from the remainder of the dune by the gravel road (area 2). The eastern dune nearer the brook contained 494 plants. In total, the Lower Bow site contained 789 plants (area 3).

Plants are not evenly distributed around the dunes. At area 1, 266 plants of the 293 found on this dune are concentrated along a 10 m x 20 m strip near the road on the southern dune area. Of these 266 plants, 247 plants were found on the southern and northern dune slopes, 19 along the dune crest. The remaining 27 plants are scattered along the northern dune crest area. No plants were found along the eastern lower dune slopes or crests. At area 3, two plants were found at the southern dune crest. At area 2, 407 of the 494 plants were located within a southwestern blow-out area and along dune crests. The remaining 87 plants were distributed along the dune slopes above the inner dune circle. Typically, small-flowered sand-verbena is found on higher slopes of partly stabilized dune areas. Usually, there is significant open sand at these sites.

North of Medicine Hat (figure 4 site 5)

This site was included in the original report (Smith and Bradley 1992) and had been found by Johnson (1975). This is estimated to have about 100 plants.

North of Medicine Hat Suffield (figure 4 site 6)

In 2002, another investigator, Garry Trottier, discovered a new site on Canadian Forces Base Suffield north of Medicine Hat. (Garry Trottier, pers. com., September 2002). Trottier discovered three nearby locations with a total population count of 100 plants. The population counts for these sites were as follows: Location 1 (Fish Creek): 80 plants in groupings of 48, 29, 1 and 2 plants; Location 2 (Down-river from Location 1): 19 plants in groupings of 17 and 2 plants; and Location 3 (Koomati): 1 plant. (Trottier 2002).

Suffield National Wildlife Area (figure 4 site 7)

Macdonald (1994) reported 1 plant at the Suffield National Wildlife Area site.

Saskatchewan

Only one other Canadian small-flowered sand-verbena site exists outside Alberta. This site lies just east of the Alberta/Saskatchewan along the South Saskatchewan River in Saskatchewan. John H. Hudson located ten plants at this site in 1981 and describes it as a steep sloping cutbank on loose sand (figure 4 site B).

 The Saskatchewan site was surveyed by Sheila Lamont and Wayne Harris from Saskatchewan in August 2002. The dune site lying west of the South Saskatchewan River but east of the Alberta/Saskatchewan border was surveyed but no small-flowered sand-verbena plants were found. An abundance of other annuals was noted during the survey of the dune area. (Candace Elchuk, personal communication, Sept. 16, 2002)